1. Field of the Invention
The present invention relates to an air intake system of an engine and more particularly to an air intake system of an engine having a tumble generating valve for generating tumble stream in a combustion chamber of the engine.
2. Discussion of Related Arts
It is well known that the combustion condition of an internal combustion engine enhances when a tumble stream is generated in a combustion chamber of the engine. When the combustion condition enhances, miscellaneous advantages such as an improvement of startability of an engine, an improvement of exhaust emissions by making a lean mixture condition and the like, are provided.
Japanese Patent Application Laid-open No. Toku-Kai-Hei 5-209582 discloses an air intake system in which an intake port is divided into two parts, a light load port and a heavy load port, by a partition and a tumble generating valve is provided on the heavy load port side. A fuel injector is disposed opposite to the partition such that injected fuel collides against the partition directly and a part of the partition against which fuel collides is shaped in convex and concave so as to enhance atomization of fuel.
The tumble generating valve (hereinafter referred to as TGV) is closed at starting. That is, at starting, in order to enhance startability or to make lean air-fuel mixture, air-fuel mixture is supplied only from the light load port side with the TGV closed so as to generate a tumble stream in the combustion chamber. Further, from the view point of reducing cranking time, it is desirable that the TGV has been closed before the ignition switch is turned on in order to delete time lag necessary for closing the TGV when the ignition switch is turned on. Hence, the TGV is closed when the engine stops and is maintained in a closed condition until the engine is started again.
However, when the TGV is left closed while the engine is in standstill, the engine is cooled down and as a result the TGV is apt to be stained with oil, residues and the like. Further, when temperature is low, the TGV might be frozen by water. As a result, there is a problem that the TGV is stuck due to stains or frozen water.
One solution of this problem is that the TGV is left open when the engine is in standstill. However, since it is necessary to close the TGV once when the engine is started, the starting time is elongated by an operation time (0.5 to 1.0 second) of the TGV from an open to closed condition. This elongation of starting time provides a driver with a bad operational feeling and spoils a customer""s satisfaction. Accordingly, the structure of the TGV remaining open can not introduced easily.
It is an object of the present invention to provide an air intake system having a tumble generating valve (TGV) capable of preventing a faulty operation without spoiling startability of an engine.
To attain the object, an air intake system of an internal combustion engine having an intake passage divided into a first passage and a second passage downstream of a throttle valve and a control valve provided in the first passage for controlling a flow of air comprises an electronic control unit provided to open and hold the control valve at a specified opening angle while the engine is inoperative after the engine is stopped. Also, the electronic control unit of the air intake system is adopted to fully close the control valve before opening the control valve at the specified angle.